How much radiation
do we get?

The average person in the United States
receives about 360 mrem every year whole body equivalent dose. This is
mostly from natural sources of radiation, such as radon. (See Radiation
and Us ).

In 1992, the average dose received by nuclear
power workers in the United States was 3 mSv whole body equivalent in
addition to their background dose.

What is the
effect of radiation?

Radiation causes ionizations in the molecules
of living cells. These ionizations result in the removal of electrons
from the atoms, forming ions or charged atoms. The ions formed then can
go on to react with other atoms in the cell, causing damage. An example
of this would be if a gamma ray passes through a cell, the water molecules
near the DNA might be ionized and the ions might react with the DNA causing
it to break.

At low doses, such as what we receive every
day from background radiation, the cells repair the damage rapidly. At
higher doses (up to 1 Sv), the cells might not be able to repair the damage,
and the cells may either be changed permanently or die. Most cells that
die are of little consequence, the body can just replace them. Cells changed
permanently may go on to produce abnormal cells when they divide. In the
right circumstance, these cells may become cancerous. This is the origin
of our increased risk in cancer, as a result of radiation exposure.

At even higher doses, the cells cannot be
replaced fast enough and tissues fail to function. An example of this
would be "radiation sickness." This is a condition that results after
high acute doses to the whole body (>2 Gy), the body's immune system
is damaged and cannot fight off infection and disease. Several hours after
exposure nausea and vomiting occur. This leads to nausea, diarrhea and
general weakness. With higher whole body doses (>10 Gy), the intestinal
lining is damaged to the point that it cannot perform its functions of
intake of water and nutrients, and protecting the body against infection.
At whole body doses near 7 Gy, if no medical attention is given, about
50% of the people are expected to die within 60 days of the exposure,
due mostly from infections.

If someone receives a whole body dose more
than 20 Gy, they will suffer vascular damage of vital blood providing
systems for nervous tissue, such as the brain. It is likely at doses this
high, 100% of the people will die, from a combination of all the reasons
associated with lower doses and the vascular damage.

There a large difference between whole body
dose, and doses to only part of the body. Most cases we will consider
will be for doses to the whole body.

What needs to be remembered is that very
few people have ever received doses more than 2 Gy. With the current
safety measures in place, it is not expected that anyone will receive
greater than 0.05 Gy in one year where these sicknesses are for sudden
doses delivered all at once. Radiation risk estimates, therefore, are
based on the increased rates of cancer, not on death directly from the
radiation.

Non-Ionizing radiation does not cause damage
the same way that ionizing radiation does. It tends to cause chemical
changes (UV) or heating (Visible light, Microwaves) and other molecular
changes (EMF). Further information on EMF that may be of interest.

Risk

How is risk
determined?

Risk estimates for radiation were first
evaluated by scientific committees in the starting in the 1950s. The most
recent of these committees was the Biological Effects of Ionizing Radiation
committee five (BEIR V). Like previous committees, this one was charged
with estimating the risk associated with radiation exposure. They published
their findings in 1990. The BEIR IV committee established risks exclusively
for radon and other internally alpha emitting radiation, while BEIR V
concentrated primarily on external radiation exposure data.

It is difficult to estimate risks from radiation,
for most of the radiation exposures that humans receive are very close
to background levels. In most cases, the effects from radiation are not
distinguishable from normal levels of those same effects. With the beginning
of radiation use in the early part of the century, the early researchers
and users of radiation were not as careful as we are today though. The
information from medical uses and from the survivors of the atomic bombs
(ABS) in Japan, have given us most of what we know about radiation and
its effects on humans. Risk estimates have their limitations,

The doses from which risk estimates are derived were much higher than
the regulated dose levels of today;

The dose rates were much higher than normally received;

The actual doses received by the ABS group and some of the medical
treatment cases have had to be estimated and are not known precisely;

Many other factors like ethnic origin, natural levels of cancers,
diet, smoking, stress and bias effect the estimates.

What is the
risk estimate?

According to the Biological Effects of Ionizing
Radiation committee V (BEIR V), the risk of cancer death is 0.08% per
rem for doses received rapidly (acute) and might be 2-4 times (0.04% per
rem) less than that for doses received over a long period of time (chronic).
These risk estimates are an average for all ages, males and females, and
all forms of cancer. There is a great deal of uncertainty associated with
the estimate.

Risk from radiation exposure has been estimated
by other scientific groups. The other estimates are not the exact same
as the BEIR V estimates, due to differing methods of risk and assumptions
used in the calculations, but all are close.

Risk comparison

The real question is: how much will radiation
exposure increase my chances of cancer death over my lifetime.

To answer this, we need to make a few general
statements of understanding. One is that in the US, the current death
rate from cancer is approximately 20 percent, so out of any group of 10,000
United States citizens, about 2,000 of them will die of cancer. Second,
that contracting cancer is a random process, where given a set population,
we can estimate that about 20 percent will die from cancer, but we cannot
say which individuals will die. Finally, that a conservative estimate
of risk from low doses of radiation is thought to be one in which the
risk is linear with dose. That is, that the risk increases with a subsequent
increase in dose. Most scientists believe that this is a conservative
model of the risk.

So, now the risk estimates. If you were
to take a large population, such as 10,000 people and expose them to one
rem (to their whole body), you would expect approximately eight additional
deaths (0.08%*10,000*1 rem). So, instead of the 2,000 people expected
to die from cancer naturally, you would now have 2,008. This small increase
in the expected number of deaths would not be seen in this group, due
to natural fluctuations in the rate of cancer.

What needs to be remembered it is not known
that 8 people will die, but that there is a risk of 8 additional deaths
in a group of 10,000 people if they would all receive one rem instantaneously.

If they would receive the 1 rem over a long
period of time, such as a year, the risk would be less than half this
(<4 expected fatal cancers).

Risks can be looked at in many ways, here
are a few ways to help visualize risk.

One way often used is to look at the number
of "days lost" out of a population due to early death from separate causes,
then dividing those days lost between the population to get an "Average
Life expectancy lost" due to those causes. The following is a table of
life expectancy lost for several causes:

Health Risk

Est. life expectancy
lost

Smoking 20 cigs a day

6 years

Overweight (15%)

2 years

Alcohol (US Ave)

1 year

All Accidents

207 days

All Natural Hazards

7 days

Occupational dose (300
mrem/yr)

15 days

Occupational dose (1
rem/yr)

51 days

You can also use the same approach to looking
at risks on the job:

Industry type

Est. life expectancy
lost

All Industries

60 days

Agriculture

320 days

Construction

227 days

Mining and quarrying

167 days

Manufacturing

40 days

Occupational dose (300
mrem/yr)

15 days

Occupational dose (1
rem/yr)

51 days

___________________

These are estimates taken from the NRC Draft guide DG-8012 and were adapted
from B.L Cohen and I.S. Lee, "Catalogue of Risks Extended and Updates",
Health Physics, Vol. 61, September 1991.

Another way of looking at risk, is to look at the Relative Risk of 1
in a million chances of dying of activities common to our society.

Smoking
1.4 cigarettes (lung cancer)

Eating
40 tablespoons of peanut butter

Spending
2 days in New York City (air pollution)

Driving
40 miles in a car (accident)

Flying
2500 miles in a jet (accident)

Canoeing
for 6 minutes

Receiving
10 mrem of radiation (cancer)

Adapted from DOE Radiation Worker Training, based on work by B.L Cohen,
Sc.D.

The following is a comparison of the risks of some medical exams and
is based on the following information:

Cigarette
Smoking - 50,000 lung cancer deaths each year per 50 million
smokers consuming 20 cigarettes a day, or one death per 7.3 million
cigarettes smoked or 1.37 x 10-7 deaths per cigarette

Highway
Driving - 56,000 deaths each year per 100 million drivers, each
covering 10,000 miles or one death per 18 million miles driving,
or 5.6 x 10-8 deaths per mile driven

Adapted from information in Radiobiology
for the Radiologist, Forth Edition; Eric Hall 1994, J.B. Lippincott
Company

So, in summary, we must balance the risks
with the benefit. It is something we do often. We want to go somewhere
in a hurry, we accept the risks of driving for that benefit. We want to
eat fat foods, we accept the risks of heart disease. Radiation is another
risk which we must balance with the benefit. The benefit is that we can
have a source of power, or we can do scientific research, or receive medical
treatments. The risks are a small increase in cancer. Risk comparisons
show that radiation is a small risk, when compared to risks we take every
day. We have studied radiation for nearly 100 years now. It is not a mysterious
source of disease, but a well-understood phenomenon, better understood
than almost any other cancer causing agent to which we are exposed.

Doses

The following is a comparison of limits,
doses and dose rates from many different sources. Most of this data came
from Radiobiology for the Radiologist, by Eric Hall or BEIR V, National
Academy of Science. Ranges have been given if known. All doses are TEDE
(whole body total) unless otherwise noted. Units are defined on our Terms
Page. The doses for x-rays are for the years 1980-1985 and
could be lower today. Any correction or comments can be sent to us at
the University of Michigan using our comment
form.